This invention relates generally to the use of a single housing detector device for sensing movement of the device and signaling an alarm signal in a security system, and in particular, in a first aspect, to a single housing wireless sensor that detects a change in the position of a door or window to which the housing is attached by detecting a change in the magnetic field of the earth. In a second aspect, an alarm device senses changes in position of the housing with respect to the surrounding gravitational field in order to trigger an alarm in a security system.
Conventional door or window sensors in security systems contain two housings; one housing with a magnet, and one housing with a sensor such as a reed switch, which is a miniature encapsulated switch that is activated by a magnetic field. One of the housings is mounted to the door or window (entrance closure) being monitored and the other housing is mounted to the doorjamb or windowsill associated with the entrance closure being monitored. When the entrance closure is closed and the magnet is in close proximity to the reed switch sensor, the sensor produces an output signal that indicates that the door is in its closed position. Once the entrance closure is moved the magnet is not in close proximity to the reed switch sensor and the sensor produces an output signal that indicates the door is not in its closed position. The output signal is periodically read by the alarm system controller, and when the signal indicates that the door is not in its closed position, the alarm system controller activates an alarm condition. The alarm system controller may receive this information through wired or wireless transmission. Alarm systems of this type are described in U.S. Pat. Nos. 4,677,424; 4,339,747; 3,896,427; 3,668,579; 4,359,719; and 4,241,337.
Alarm systems using reed switch sensors, as described above, are reasonably successful in many applications, although there are a number of drawbacks as follows:
1) There is additional cost and time, during installation, for the installer to mount a second device (i.e. the magnet).
2) The position of the magnet in conjunction with the sensor is often critical and the installer spends time shimming and locating the magnet to optimize the reed to magnet gap.
3) Reed switches, which are glass encapsulated switches are fragile and may be damaged at the time of installation.
4) Sensors with two housings can be defeated during the period when the system is in the disarmed state by the addition of an extra magnet taped to the sensor housing. This maintains the reed in its closed position even if the door is opened during an armed state.
It is therefore an object of the design to deliver improved security to the system, since any attempt to tamper with the device by adding a magnet would cause an alarm condition.
It is therefore an object of the present invention to provide an entrance closure sensor that is contained in a single housing.
It is a further object of the present invention to provide an entrance closure sensor with improved sensor reliability.
In another aspect of the field of motion detection, sensors designed for asset protection monitor the asset""s location to determine if it is where it should be. If it is determined that the asset is not where it should be, an alarm signal is annunciated. The asset could be an object or a person. For the object, such as a laptop computer, protection would be to determine that the computer has not left the premises without authorization. For a person, such as a firefighter or elderly relative, protection would be to determine that the person was still upright and moving when they should be.
Others have developed devices to perform this task but these devices are either overly complex, expensive, unreliable, or difficult to use. One such device tracks objects by monitoring a marker affixed to the object that periodically sends RF identification signals. Sensors installed at the perimeter of the protection zone detect a breach of the perimeter when the object marker passes the sensor. Disadvantages of this system include short battery life due to the repetition rate of the transmissions and non-detection of the alarm if the asset is hidden within the premises. Another such device is a pendant worn by a person to be protected. If the person feels threatened or becomes ill they press a button on the pendant to annunciate the alarm. A disadvantage of this system is if the person becomes disabled and is unable to press the button, no alarm will be annunciated. Another device similar to our invention uses a dual-axis accelerometer mounted in a notebook PC card that monitors the motion of the PC. If the PC travels a certain distance the PC is disabled. This system differs from ours because it is not wireless, it is not battery powered, there is no alarm annunciation, and its detection method is based the acceleration due to on motion, not the gravitational attraction to the Earth as in our invention.
It is therefore a further object of the invention to provide a device that can sense the movement of an object or person with which the device is associated; i.e. by attachment.
In accordance with these and other objects, the present invention in a first aspect is a method, an apparatus, and a system for detecting a change in position of an entrance closure in an alarm system, wherein the entrance closure is either a door or a window.
The method of this first aspect of the invention comprises the steps of attaching a singular housing on an entrance closure; monitoring, with apparatus in the housing, the magnetic field of the earth, detecting a change in the position of the housing with respect to the magnetic field of the earth, generating an alarm signal upon detecting a change in position of the housing with respect to the magnetic field of the earth that exceeds a first predetermined threshold, and transmitting by wireless transmission the alarm signal to a remote receiving station.
The apparatus of this first aspect of the invention comprises a singular housing with means for monitoring the magnetic field of the earth, means for detecting a change in the position of the housing with respect to the magnetic field of the earth, means for generating an alarm signal upon detecting a change in position of the housing with respect to the magnetic field of the earth, and means for transmitting by wireless transmission the alarm signal to a remote receiving station. The alarm signal may contain a programmable unique transmitter identification number that allows the receiving station to decipher which sensor has sent the alarm message. The monitoring of the magnetic field of the earth is performed by a magnetometer that senses the earth""s magnetic field and generates an output signal correlated to the earth""s magnetic field. A microprocessor detects a change in the position of the housing by sampling the magnetometer""s output signal at predetermined intervals and determining if the sampled output is different from a stored static (initial) output. If the sampled output is different from the stored static output by a first predetermined amount the microprocessor generates an alarm signal and causes the alarm signal to be transmitted. In addition, if the sampled output is different from the stored static output by a second predetermined amount, the microprocessor generates a trouble signal, wherein the second predetermined amount is less than the first predetermined amount. This may occur when the door or window is slightly ajar. This feature is useful to a user during arming of the alarm system, wherein the user can ensure the entrance enclosures are closed prior to vacating the premises being monitored.
The alarm system of this first aspect of the invention comprises the apparatus described above for detecting a change in position of an entrance closure, and a receiving station, located remotely from the apparatus. The receiving station comprises means for receiving by wireless transmission the alarm signal from the apparatus, and means for indicating an alarm condition in response to the receipt of the alarm signal.
The step of detecting a change in the position of the housing with respect to the magnetic field of the earth may take place on three axes and the generation of an alarm signal may occur upon detecting a change in position of the housing in two of the three axes.
In order to provide security with less false alarms, the remote receiving station may correlate the alarm signal from the apparatus of the present invention with a second alarm signal from a different sensor, which may be a motion sensor.
In a second aspect of the invention in this field of motion detection, a sensor that detects changes in the earth""s gravitational field is used to detect motion. The method comprises the steps of locating a housing with respect to an object; monitoring, with apparatus in the housing, the gravitational field of the earth; detecting a change in the position of the housing with respect to the gravitational field of the earth; generating an alarm signal upon detecting a change in position of the housing with respect to the gravitational field of the earth that exceeds a first predetermined threshold, and transmitting by wireless transmission the alarm signal to a remote receiving station.
The housing is located with respect to the object, for example, by affixing the housing to the object (such as by attaching it to a valuable painting, a laptop computer, etc.). The housing may also be hung from an object, such as by placing it on a chain around a person""s neck, or around the person""s wrist, etc.
The apparatus of this second embodiment comprises a housing with means for monitoring the gravitational field of the earth, means for detecting a change in the position of the housing with respect to the gravitational field of the earth, means for generating an alarm signal upon detecting a change in position of the housing with respect to the gravitational field of the earth, and means for transmitting by wireless transmission the alarm signal to a remote receiving station. The alarm signal may contain a programmable unique transmitter identification number that allows the receiving station to decipher which sensor has sent the alarm message. The monitoring of the gravitational field of the earth is performed by a device that senses the earth""s gravitational field and generates an output signal correlated to the earth""s gravitational field. A processor detects a change in the position of the housing by sampling the output signal at predetermined intervals and determining if the sampled output is different from a stored static (initial) output by a predetermined amount. If the sampled output is different from the stored static output by a first predetermined amount the microprocessor generates an alarm signal and causes the alarm signal to be transmitted. In addition, if the sampled output is different from the stored static output by a second predetermined amount, the microprocessor generates a trouble signal. The second predetermined amount may be less than the first predetermined amount.